1. Field of the Invention
The present invention relates to an engine. Particularly, an improvement of an engine including a crankshaft having first and second journals disposed at opposite ends of the crankshaft. An engine block has a crankcase with a first bearing to support the first journal on one sidewall and an opening is provided in the other sidewall to facilitate assembly of the crankshaft. A case cover is coupled to the crankcase by a plurality of bolts to close the opening.
2. Description of the Related Art
Such an engine is known, as disclosed, for example, in Japanese Utility Model Publication No.3-49996.
In order to define a position for coupling the crankcase and the case cover to each other in the engine, it is conventional practice to fit knock pins into at least two positioning bores which open into joint faces of the crankcase and the case cover. The two knock pins are disposed on opposite sides of the axis of the crankshaft. The knock pins are used exclusively to define the position for coupling the crankcase and the case cover to each other.
Accordingly, it is an object of the present invention to provide an engine which is constructed with a durability in such a manner that at least two knock pins fit into the crankcase and the case cover over their joint faces not only define the position for coupling of the crankcase and the case cover to each other, as in the conventional engine described above, but also increase the rigidity of the case cover.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided an engine including a crankshaft having first and second journals disposed at opposite ends thereof. An engine block has a crankcase with a first bearing that supports the first journal on one sidewall and an opening is provided in the other sidewall to facilitate assembly of the crankshaft. A case cover is coupled to the crankcase by a plurality of bolts to close the opening. A second bearing is also provided to support the second journal, wherein at least two knock pins are fitted into the crankcase and the case cover over their joint faces at locations closer to a cylinder bore in the engine block than the second bearing.
The first and second bearings correspond to first and second bearing bushes in an embodiment of the present invention, which will be described hereinafter. With the above arrangement, when an explosion load is applied from the crankshaft to the case cover during an explosion stroke of the engine, a tensile stress is generated on the case cover over a wide area between the second bearing and the two knock pins. At this point, the case cover, which has a strong resistance to the tensile stress, can exhibit a high rigidity. Therefore, the two knock pins define the position for coupling the crankcase and the case cover to each other, and moreover increase the rigidity of the case cover. Thus, it is possible to increase the supporting strength for the crankshaft while reducing the weight of the case cover.
According to a second aspect and feature of the present invention, in addition to the first feature, the two knock pins are substantially equidistantly positioned on opposite sides of a plane that includes an axis of a cylinder bore and an axis of the crankshaft.
With the above arrangement, it is possible to equalize the shearing load applied to each knock pin and disperse the tensile stress in the case cover, thereby enhancing the durability of the knock pins and the case cover.
According to a third aspect and feature of the present invention, in addition to the first or second features, one of the knock pins is hollow. An oil passage in the engine block and an oil passage in the case cover communicate with each other through a hole in the hollow knock pin.
With the above arrangement, one of the hollow knock pins has a function of permitting communication between the oil passage in the engine block and the oil passage in the case cover. Therefore, the oil passages and the knock pin can be disposed coaxially, and thus, the disposition of the oil passage and the knock pin in the narrow joint faces can be achieved easily.
According to a fourth aspect and feature of the present invention, in addition to any of the first to third features, the knock pins are press-fit into one of the crankcase and the case cover.
With the above arrangement, a fitting gap for the knock pins is provided only between each knock pin and the other of the crankcase and the case cover. Therefore, it is possible to limit dislocation between the joint faces of the crankcase and the case cover due to the relatively small fitting gap, which enhances the coupling accuracy.
The above and other objects, features and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings.